Online services allow users to perform a variety of transactions. And, while SPAM filters, antivirus software, and other techniques are used to protect members of the online services, some undesirable transactions are allowed and some desirable transactions are blocked (false positives). Furthermore, false positives occur more often with infrequent or new users because they are not known to the online services.
A number of technologies are used to reduce the damage of false positives including accreditation of large senders and the use of computational or human interactive proofs for smaller senders. Unfortunately, these technologies can be onerous or insufficient, especially for infrequent or new users.